Field of the Invention
The present invention relates to a golf ball having a core of at least one layer and a cover of at least one year. More particularly, the invention relates to a golf ball in which adhesion between the individual layers is improved, enabling the durability of the ball to cracking on impact to be increased, and to a method of manufacturing such a golf ball.
Prior Art
Solid golf balls with a multilayer construction of three or more pieces have come into frequent use in recent years, and even four-piece solid golf balls composed of a core encased by a cover of three or more layers, such as an envelope layer, an intermediate layer and an outermost layer, have made it onto the market. These multilayer golf balls are generally obtained by successively injection-molding synthetic resin cover materials around the core periphery so as to form a succession of individual layers over the core. However, when adhesion between the layers of the golf ball is poor, this may invite declines in various ball properties, such as the distance, spin rate on approach shots, feel and durability to cracking. Hence, there exists a desire to improve adhesion between the layers.
Art for improving adhesion between the layers of a golf ball includes that described in the following patent publications.
JP-A No. 10-179795 discloses art in which a layer of adhesive is formed on the intermediate layer. JP-A 11-137726 teaches art that blends an adhesive into a cover material composed primarily of a thermoplastic resin. JP-A 2003-339912 describes art wherein the surface of the inner layer in a cover having an inner layer and an outer layer is acid-washed, thereby improving adhesion between the inner layer which is made up of an ionomer resin and the outer layer which is made up of a non-ionomeric resin such as a polyurethane elastomer. Finally, JP-A 2009-131631 discloses a golf ball manufacturing method wherein, to improve adhesion between a rubber core and a urethane cover, the surface of the rubber core is treated with a solution containing a haloisocyanuric acid and/or a metal salt thereof, following which the treated core is encased with the cover material.
However, depending on the materials of which the individual layers are made, adhesion remains inadequate even in the foregoing prior art. Adhesion is particularly inadequate between a rubber core and an ionomer-based resin material, with decreases in such adhesion having an adverse influence on various properties of the golf ball.
It is therefore an object of this invention to provide a golf ball in which adhesion between the individual layers is improved, enabling various properties of the golf ball to be enhanced, particularly the durability to cracking on impact.